With an increasing power density, thermal management becomes a more important issue in power electronic equipment. For cooling a power circuit assembly, a fan can be used. In addition, some components can be directly attached to a heat sink. In particular, a power module, which can be the main contributor to losses in power electronic equipment, is mounted directly onto a heat sink to keep the semiconductor temperatures in an acceptable range.
If other components, such as control electronics, an auxiliary supply, balancing resistors and the like would be attached to the same heat sink, there would be a risk that these other components are overheated by excessive heat from the power module, instead of being cooled. Cooling of these other components can be performed by a separate cooling mechanism, such as by attaching them to the housing or to another heat sink. However, this increases the complexity of the equipment since several cooling paths now have to be implemented and considered. This may also lead to restrictions on where such power equipment can be placed.
These issues are particularly relevant in the case of a power circuit assembly having a high ingress protection class. For many applications, such as the food and beverage industry, a high ingress protection class (IP class) is involved. In those high IP classes, the electronic components are enclosed by a sealed housing, and thus provided in a so-called clean room which is provided inside the housing and thus separated from the outside (dirty room) by the housing. This leads to additional restrictions on the cooling.
Further, capacitors in a power circuit assembly may not be placed freely, if additional stray capacities and/or parasitic inductances due to their electrical wiring are to be avoided, for example, to keep over-voltages and switching losses small. The capacitors may then need to be placed close to the power module for avoiding such stray capacities. This requirement, combined with the necessity of separate cooling, can result in an arrangement where the capacitors are standing on top of the circuit main board, which allows a wiring with minimum parasitic inductances. The capacitor may then be cooled by means of a fan. With this arrangement, the capacitors define the minimum height of the housing due to their shape (e.g., cylinders with height larger than diameter). The resulting large volume of the housing directly limits the power density of the converter.